条件选择字段值

Question

我正在为体育游戏创建一个数据库。

我有一个名为游戏的表：

-----------------------------
winner  | team_id1 | team_id2
-----------------------------

我有一个表团队

----------
id | title
----------

如果winner = 1，team_id1是获胜者团队的id

如果winner = 2，team_id2是获胜者团队的id

最后，我希望每场比赛都获得冠军队的头衔，然后是失败者队的头衔。

尝试了类似的事情：

select tea1.title, tea2.title
from games gam
join teams tea1 on case
when gam.winner = 1 and gam.team1_id = tea1.id then 1
when gam.winner = 2 and gam.team2_id = tea1.id then 1
else 0
end = 1
join teams tea2 on case
when gam.winner = 2 and gam.team1_id = tea2.id then 1
when gam.winner = 1 and gam.team2_id = tea2.id then 1
else 0
end = 1

但请求挂起，我不明白为什么。

Answer 1

尝试在select子句而不是连接条件中获得赢家或输家。

select
    gam.winner,
    case when gam.winner=1 then t1.title else t2.title end as winner_title,
    case when gam.winner=2 then t1.title else t2.title end as loser_title
from
    games gam
left join
    teams t1
on
    gam.team1_id = t1.id
left join
    teams t2
on
    gam.team2_id = t2.id